Look for the C-Language Copy of UIApplicationMain
Look for the C-Language Copy of UIApplicationMain

A long while back we added a copy of UIApplicaitonMain to the UIKit
overlay. This was intended to fix the signature of UIApplicationMain by
forcing clients to choose a non-deprecated copy with revised nullability
annotations that were compatible with the (then) interface of the (then)
CommandLine stdlib type. Since then, we've gone in a completely different
direction with type-based entrypoints and @main, but the compatibility
shims remain. This code was assuming that it would always find one
declaration of UIApplicationMain in the clang module, but that's not
a sound assumption to make. In certain scenarios, we can wind up finding
the overlay's copy of UIApplicationMain too. When that's the Swift
function, we reference a native-to-foreign thunk that we don't actually
wind up generating in the open-coding and this results in a nasty linker
error. Filter the available candidates here looking for the C copy of
UIApplicationMain.

rdar://101932338

apple/swift,apple/swift,apple/swift,apple/swift,apple/swift,apple/swift